Prepare and bake cake according to package directions, using two greased and waxed paper-lined 9" round pans. Cool for 10 minutes before removing from pans to wire racks to cool completely; carefully remove waxed paper.
Level tops of cakes. Spread frosting between layers and over the top and sides of the cake.
Without separating Peeps and curving slightly to fit, arrange chicks around edge of cake for sunflower petals. For sunflower seeds, arrange chocolate chips in center of cake.